论文标题

元素独特性和通过伪随机设定交点的时间空间权衡

Time-Space Tradeoffs for Element Distinctness and Set Intersection via Pseudorandomness

论文作者

Lyu, Xin, Zhu, Weihao

论文摘要

在元素独特性问题中,给出了一个数组$ a_1,\ dots,a_n $来自$ [poly(n)] $的整数的a_n $,并要求决定$ \ {a_i \} $是否相互不同。 Beame,Clifford和Machmouchi(Focs 2013)给出了在空间中运行的此问题的低空算法,其中$ t(n)\ le \ le \ widetilde {o} {o}(n^{n^{3/2}/s(3/2}/s(n)/s(n)^n) Chen,Jin,Williams和Wu(Soda 2022)的最新突破展示了如何删除政权$ s(n)= polylog(n)$和$ t(n)= \ widetilde {o}(n^{3/2}})$中的随机甲骨文假设。他们设计了第一个真正的$ polygog(n)$ - space,$ \ widetilde {o}(n^{3/2})$ - 时间算法,通过构造一个小家族hash函数$ \ mathcal {h} h:具有某个pseudorandom属性的[poly(n)] \ to [n] \} $。 在本文中,我们对Chen等人对伪随机汉族家族进行了显着简化的分析。我们的分析清楚地确定了欺骗BCM算法所需的关键伪型属性,从而使我们能够探索这种构建的全部潜力。作为我们的主要结果,我们在没有随机甲骨文的情况下显示了元素独特性的时空权衡。也就是说,对于每$ s(n),t(n)$,使$ t \ of bout d \ wideTilde {o}(n^{3/2}/s(n)^{1/2})$,我们的算法可以在太空中解决问题$ s(n)$ s(n)$ t(n)$ t(n)$。我们的算法也适用于相关的问题集交叉点,由于Dinur的匹配下限(Eurocrypt 2020),此折衷是紧张的。作为另外两个贡献,我们展示了哈希家族的更一般的伪和性能,并稍微改善了种子长度,以品尝伪哈希函数。

In the Element Distinctness problem, one is given an array $a_1,\dots, a_n$ of integers from $[poly(n)]$ and is tasked to decide if $\{a_i\}$ are mutually distinct. Beame, Clifford and Machmouchi (FOCS 2013) gave a low-space algorithm for this problem running in space $S(n)$ and time $T(n)$ where $T(n) \le \widetilde{O}(n^{3/2}/S(n)^{1/2})$, assuming a random oracle (i.e., random access to polynomially many random bits). A recent breakthrough by Chen, Jin, Williams and Wu (SODA 2022) showed how to remove the random oracle assumption in the regime $S(n) = polylog(n)$ and $T(n) = \widetilde{O}(n^{3/2})$. They designed the first truly $polylog(n)$-space, $\widetilde{O}(n^{3/2})$-time algorithm by constructing a small family of hash functions $\mathcal{H} \subseteq \{h | h:[poly(n)]\to [n]\}$ with a certain pseudorandom property. In this paper, we give a significantly simplified analysis of the pseudorandom hash family by Chen et al. Our analysis clearly identifies the key pseudorandom property required to fool the BCM algorithm, allowing us to explore the full potential of this construction. As our main result, we show a time-space tradeoff for Element Distinctness without random oracle. Namely, for every $S(n),T(n)$ such that $T\approx \widetilde{O}(n^{3/2}/S(n)^{1/2})$, our algorithm can solve the problem in space $S(n)$ and time $T(n)$. Our algorithm also works for a related problem Set Intersection, for which this tradeoff is tight due to a matching lower bound by Dinur (Eurocrypt 2020). As two additional contributions, we show a more general pseudorandom property of the hash family, and slightly improve the seed length to sample the pseudorandom hash function.

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